A conventional power-operated jaw chuck can have a base for mounting it during use upon the operational spindle of a lathe headstock, or a like machine tool. The base then is substantially coaxial with respect to the spindle about the axis of which it is rotated.
The clamping jaws of the chuck are radially guided in a chucking head on this base, so as to be movable toward and away from a clamping axis which is parallel to the axis of rotation but can be offset therefrom for eccentric chucking. Axially movable wedge members serve to connect the clamping jaws to a drive piston.
The chuck also has a holding body which is adjustably guided at the base, i.e., in a direction transverse to the axis of rotation, and also in a direction parallel to a plane through the axis of rotation and the clamping axis.
The assembly further includes counterbalancing elements which can move in the same direction as the holding body.
This chuck makes it possible to turn crankshafts and other eccentric workpieces on a lathe with a fairly constant chucking diameter, but with varying crank or crank-stroke distances. However, adaptation to other chucking diameters or distances is only possible through replacement of mounting elements which are mounted on the chuck jaws or jaws mounted on movable jaw carriers.
In general terms, the chuck base is a flanged element which allows coupling of the unit to the spindle of the respective lathe, and the head is guided by corresponding means so as to be movable with respect to the base. The head could also be secured in place or clamped against the base, by means of a control spindle and a shim, or similar element, which controls its position.
The clamping jaws and their wedge elements are guided in the head, with the wedge elements being connected to the drive piston. The clamping plate serves to connect the wedge elements and the drive piston. These wedge elements are positively connected in an axial direction, but they may be shifted in the displacement or shifting direction of the chuck head.
In addition, workpiece retainers were arranged in the head, and these retainers align the workpiece prior to its clamping. For this, each retainer has a pair of guide or orienting jaws which also serve to guide the movable jaw at the chuck head.
A separate and axially movable wedge element is provided for actuation of this guide jaw. The separate wedge element, in a manner analogous to that of the wedge elements for the clamping jaws, is hung on a second clamping plate. The second clamping plate is connected to a second drive piston which exclusively serves to move the guide jaw. This second drive piston is guided in the base and it is adapted to extend coaxially with respect to the clamping piston for the clamping jaws, and coaxially with respect to the axis of rotation of the base.
In the final analysis, the chuck head, excepting the clamping plates and the drive pistons, form a full chuck assembly or unit which, in conformity with the crank distance of the workpiece, can be adjusted at the chuck base.
The counterbalancing weights are arranged at the head so as to be movable. They serve to compensate for the imbalances arising at the base upon displacements or shifting of the head. Accordingly, they can be displaced in an opposing or counter-directed manner at the head in conformity with the position in and in relation to the head. The counterbalancing weights can be clamped against the head in their respective positions by way of an associated spindle and spacers or shims.
These known chucks have the drawback that the mass of the adjustable chuck head is rather large and the mass of the attendant counterbalancing weights needs to be proportionally large. Remaining imbalances--to be absorbed by the bearings for the lathe spindle or spindles--are still relatively large, and this stresses the spindle bearings correspondingly.
Furthermore, the adjustment of the head and the counterbalancing weights is cumbersome and difficult because these associated adjustments require separate operational steps. Also, after each adjustment there is need for separate tightening or clamping for fixing the adjustment position, and this additional effort oftentimes is not without adverse affect on the accuracy of the adjustment itself.